1. Field of the Invention
The present invention pertains to apparatus for controlling flow of fluids from an oil and/or gas well. In particular, it pertains to apparatus commonly referred to as "chokes" for controlling the flow of fluids from an oil and/or gas well. More specifically, the present invention pertains to drilling chokes for controlling the flow of fluids from a well as such well is being drilled.
2. Background of the Invention
During the drilling of an oil and/or gas well, the drill string may penetrate into a high pressure gas pocket which when encountered seeks relief through the drill string and surrounding hole to the surface of the earth. If the pressure and/or volume of gas is sufficient, drilling fluids are carried to the surface with the gas and could cause potential loss of control of the well. In fact, the drill string may be blown out of the well and portions of the drilling unit destroyed. Of course, such occurrence may also result in death or serious injury to drilling personnel.
To prevent such loss of well control, various control apparatus are provided. Blowout preventers may be provided for closing the annulus around the drill string. Another control device is the drilling choke. There are a number of types of drilling chokes, but basically these chokes usually include a body having an inlet and an outlet, the outlet of which is provided with a seat assembly. Also included is a stem assembly on the end of which is a tip capable of sealing engagement with the seat assembly. An operator assembly, usually hydraulically or pneumatically operated, moves the stem assembly to various positions, causing the flow of fluids from the well to be regulated by the variable flow passage created by the seat assembly and the stem.
The amount of flow allowed through the drilling choke may be automatically or manually controlled based on the fluid pressures and volumes encountered during drilling. Drill pipe pressure, choke manifold pressure, choke position and various other information is usually indicated at a position on the drilling rig to enable the operator to control the well.
Drilling chokes are manufactured by a number of companies including Cameron Iron Works, Inc.; Thornhill-Craver Co., Inc.; N.L. Industries, Inc., all of Houston, Tex., and others. Due to the high pressures, high volumes and abrasive characteristics of drilling fluids, some of the internal components of a drilling choke, particularly the seat and stem assemblies, require frequent repair or replacement. To replace or repair the seat assembly or the stem assembly of a drilling choke, it is normally necessary to first remove the operator assembly from the choke body. Then the seat assembly and stem assembly can be reached for such repair or replacement. To remove the stem assembly, it is normally necessary to disturb the pneumatic or hydraulic portions of the operator assembly causing the loss of the operator assembly fluids. This is time-consuming, messy and costly, among other things.
Furthermore, most drilling chokes are provided with some type of position indicator which is attached to the operator assembly. In fact, most drilling chokes are provided with a position rod which is coaxially aligned with the stem assembly, but projects in the opposite direction from the operator assembly. This results in undue length, bulkiness and complexity of the choke. For example, due to the fact that the position rod projects out of the operator assembly, usually from a piston carried therein, additional seals and sealing surfaces are required. This is more expensive and more susceptible to leaking.